in fact, nearly half of all voters are expected to take advantage of early voting laws. as john king reports, in the key battleground state of iowa, a favorite may already be emerging. >> we thank you ever so much for coming. >> reporter: mind made up and ballot cast 40 days early. this opening day line is in iowa city. >> here we go. >> four, five. >> reporter: this one in des moin moines. >> just scan it under the red light. >> reporter: iowa's early a voting part of an important and growing national trend. 35 states now allow some form of early in-person voting, including seven of the nine presidential battlegrounds, cnn ranks as toss-ups. here in iowa, the early numbers and early turn out suggest a big obama head start. so far, a nearly 5-1 democratic advantage statewide in requesting early mail-in ballots. >> i was wondering, mary a, if the president will have your support this november. awesome. >> reporter: there is add aed obama campaign getting numbers in the bank early. >> you may know in-person early voting starts tomorrow in iowa. so, basically for us here at